Thermostatic valves are used to automatically mix a cold water source and a hot water source to provide an output stream of the desired temperature. As the on/off and volume adjustments are downstream from the thermostatic valve, there are situations where there exists the possibility of feedthrough of hot water supply into the cold water source or vice versa. Check valves are used in the two water supply inlets to insure that such inadvertent mixing is not possible. Also, as a convenience, shutoff valves are used at the supply ports as part of the thermostatic valve. These are used when servicing the thermostatic valve itself or any system components downstream of it. The prior art devices have used separate check valves and shutoff valves along with the appropriate seals to incorporate these elements into a thermostatic valve housing.